arduino usb or arduino ethernet?
I haven't used an Ethernet shield but shield but talking to a PC with USB is a total no-brainer with Arduino, so I guess I would go that way.
So in answer to your first post, yes it's possible to monitor temperatures and report them to a PC. I'm not convinced 1-wire is good for the distances you infer (ie seperate rooms) but it might be if you use "external power" mode as is shown in figure 5 of that first link.
Rob